The present invention relates to antennas for radio signal frequencies, an electromagnetic shield, and a mechanical package for electronic components.
One of the fast growing segments of the computer industry today is wireless networks. Wireless networks avoid the cost of the wiring infrastructure, and permit computing mobility. Some of the more common wireless networks are based on the 802.11 standard, Bluetooth, cellular networks, i-mode, and WAP. Cell phones are in use nearly everywhere. Some standards such as 802.11, also known as wireless Ethernet or Wi-Fi, are also ubiquitous and can be found in many companies, offices, airports, and even coffee shops. With Wi-Fi you only need to be in range of a peer or a base station which connects the wireless network to a wired one. Thus, a person can carry Wi-Fi enabled personal digital assistant (PDA) or a notebook computer about without giving up his or her network connection. Bluetooth is another known wireless standard designed for interconnection of computing devices such as computer peripherals.
No matter what wireless standard is used, there is a fundamental need to increase antenna performance. Wireless devices emphasize compactness, however, which impacts performance. For example, if an embedded antenna is placed on a printed circuit board in close proximity to the ground plane or adjacent metal objects, the antenna performance will be degraded. The ground plane will reduce the antenna's radiation resistance, which lowers the antenna efficiency and adversely affects the antenna gain pattern. In addition, a completely shielded mechanical package will prevent the antenna from propagating the radio through the shield. Yet, the transceiver must be shielded from stray electromagnetic fields. The shield for the transceiver will also function as a ground plane in close proximity with the antenna. Again, this degrades the antenna performance. Further, the antenna performance generally increases with the length of the radiating elements of the antenna, but this means the printed circuit board will need to increase in size, which conflicts with the small size requirements of mobile devices.
FIG. 1A illustrates how an embedded antenna 14 might be configured for a cell phone to try to address these problems. As shown, the printed circuit board 20 supports a set of electronic components such as the electronic component 22. A mechanical package 10 encloses the printed circuit board 20. FIG. 1A cuts away a portion of the mechanical package 10 to show the inside of the cell phone. The antenna 14 is adjacent to an area (indicated by dotted lines 12) where the ground plane is removed in the printed circuit board 20. This removal avoids a ground plane in close proximity to the antenna 14, which would interfere with the antenna pattern. The mechanical package 10 must be also non-conductive to avoid shielding the antenna 14. Because the mechanical package 10 is non-conductive, a radiation shield 18 must enclose the RF transceiver chips 16, 17, which are sensitive to stray electromagnetic radiation. FIG. 1A also cuts away the radiation shield 18 to show the RF transceiver chips 16, 17. The antenna 14 must not be too close to electronic components on the printed circuit board 20 or to the radiation shield 18 to avoid affects on the antenna pattern. As a result of these constraints, the manufacturer will need to increase the size of the printed circuit board 20 and the mechanical package 10.
FIG. 1B illustrates how a protruding antenna 15 might be configured for a cell phone in another attempt to address these problems. The printed circuit board 20 again supports electronic components such as the electronic component 22. A mechanical package 24 encloses the printed circuit board 20, but is cut-away in FIG. 1B to show the inner arrangement. The antenna 15 is placed outside the mechanical package 24 so there is no longer the need to remove the ground plane of the printed circuit board 20 as indicated by the absence of dotted lines. The mechanical package 24 also can be conductive because it will no longer shield the antenna 15. Further, if the mechanical package 24 is non-conductive, a radiation shield 18 must enclose the RF transceiver chips 16, 17, which are sensitive to stray electromagnetic fields. FIG. 1A cuts away part of the radiation shield 18 to reveal the RF transceiver chips 16, 17. However, these advantages are dampened because the protruding antenna 15 must now be small enough to avoid user discomfort, and more rugged since it is outside the protection of the mechanical package 24. This raises the cost of the antenna 15 and limits suitable size and shapes of the antenna.
It would be desirable if an antenna could propagate electromagnetic radiation at frequencies of interest, shield against any stray electromagnetic radiation, save printed circuit space, reduce ground plane interference, and provide a rugged low cost mechanical package for the wireless device itself.